System and method for passive optical network backhaul

ABSTRACT

A system is described for providing backhaul over an Ethernet passive optical network (EPON). The backhaul may be backhaul for EV-DO and/or EV-DO Rev. A communications. The system for includes at least one cell site. At least two base transceiver stations are located at the cell site. The base transceiver stations receive radio signals from respective mobile stations. A first one of the base transceiver stations provides a first backhaul signal, and a second one of the base transceiver stations provides a second backhaul signal. The cell site multiplexes these backhaul signals together onto an Ethernet passive optical network. In one embodiment, these signals are provided on different pseudowire connections within a single wavelength lambda on the passive optical network. In another embodiment, the signals are provided on different lambdas of the network.

BACKGROUND

The present invention relates to wireless communication. In particular,the invention relates to providing a backhaul facility for wirelesscommunication.

With the ever-increasing reliance on mobile, wireless, communications,wireless service providers face the constant challenge of providingreliable service. Because packet data can not be compressed further thanit is currently compressed, packet data service providers must be ableto offer service at ever-greater bandwidths. One particularlychallenging area for service providers is securing bandwidth forbackhaul.

In providing such communications, service providers often rely on T1lines to carry backhaul for high speed wireless packet datacommunications, according to a protocol such a EV-DO Revision A, forinstance. T1 offers relatively low backhaul delay, on the order of 1 msfor each 125 miles of signal propagation. T1, however, suffers fromlimited scalability. As additional traffic is carried in a wirelesstelecommunication network, T1 lines can quickly become overburdened.This is particularly the case in a network that provides packet dataservices. As more subscribers use their mobile devices to access dataservices, the backhaul carried in a wireless network increases sharply.

EV-DO (referring to “Evolution-Data Only” or “Evolution-Data Optimized”)is one protocol for providing wireless packet data services to mobiledevices, with available download rates ranging from up to 2.5 Mb/s with(Rev. 0) to 3.1 Mb/s (Rev. A). EV-DO is described in the specification“CDMA2000 High Rate Packet Data Air Interface” EV-DO may be employed inwireless network together telephonic voice communications.

With the increasing availability to wirelessly access high-data-ratepacket data services, and with the increasing number of wirelesssubscribers, it is desirable to implement a backhaul facility thatoffers cost-effective scalability while maintaining minimal backhauldelay.

SUMMARY

A system for managing backhaul includes at least one cell site. At leasttwo base transceiver stations are located at the cell site. The basetransceiver stations receive radio signals from respective mobilestations. A first one of the base transceiver stations provides a firstbackhaul signal, and a second one of the base transceiver stationsprovides a second backhaul signal. The cell site multiplexes thesebackhaul signals together onto an Ethernet passive optical network. Inone embodiment, these signals are provided on different pseudowireconnections within a single wavelength lambda on the passive opticalnetwork. In another embodiment, the signals are provided on differentlambdas of the network.

Through the Ethernet passive optical backhaul network, the basetransceiver stations can communicate with separate mobile switchingcenters, which may be operated by separate telecommunications serviceproviders. A first one of the mobile switching centers can communicatewith the first base transceiver station through a first pseudowirecircuit over the Ethernet passive optical network, and, a second one ofthe mobile switching centers can communicate with the second basetransceiver station through a second pseudowire circuit over thenetwork.

The cell sites and mobile switching centers on the network may bearranged into a ring and/or daisy chain architecture. In this case,mobile switching centers and/or cell sites act as repeaters for signalsnot destined for them. For example, the first mobile switching centermay receive backhaul signals from both the first and second basetransceiver stations. The first mobile switching center processes thefirst backhaul signal (by connecting it with a public switched telephonenetwork, for example), but simply relays the second backhaul signaltoward the second mobile switching center. Communications on the networkmay be encrypted to prevent interception at unauthorized nodes along thenetwork.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a wireless telecommunicationnetwork including a passive optical backhaul network.

FIG. 2 is a schematic illustration of the architecture of a passiveoptical backhaul network.

FIG. 3 is a logical architectural diagram of a cell site for use in apassive optical backhaul network.

FIG. 4 is a logical architectural diagram of another cell site for usein a passive optical backhaul network.

FIG. 5 is a flow diagram illustrating a method for use in a passiveoptical backhaul network.

FIG. 6 is a flow diagram illustrating another method for use in apassive optical backhaul network.

FIG. 7 is a schematic illustration of the architecture of a passiveoptical backhaul network that makes use of a synchronous opticalnetwork.

DETAILED DESCRIPTION I. Overview of a Preferred Embodiment

FIG. 1 illustrates a system for providing backhaul to a mobile switchingcenter (MSC) 16. As illustrated in FIG. 1, a mobile device, such as amobile telephone 10 communicates wirelessly with a base transceiverstation (BTS) 14. A base station controller (BSC) 18 that services thebase transceiver station 14 forwards signals received from the mobiledevice 10 to a repeater 20. The repeater 20 is preferably a repeater onan Ethernet Passive Optical Network (EPON). Nodes on the EPONcommunicate over an optical cable 22, which may include a one or twofiber bi-directional link. Through the repeater 20 and optical cable 22,the Ethernet passive optical network provides backhaul to the mobileswitching center 16.

The base station controller 18 may service more than one basetransceiver stations, such as station 14 and one or more additionalstations 26. The Ethernet passive optical network may further includeadditional repeaters, such as repeater 28. Repeater 28 receives an inputsignal from two different base station controllers 30 and 32, whichservice respective base transceiver stations 34 and 36. Radio signalsreceived by base transceiver stations 34 and 36 are combined by amultiplexer 38 and are supplied to the repeater 28.

As illustrated in FIG. 1, the Ethernet passive optical network may havea loop architecture. Situated around the loop may be other mobileswitching centers, such as mobile switching center 24. Where more thanone mobile switching center is provided on the Ethernet passive opticalnetwork, the different mobile switching centers may be operated bydifferent wireless service providers.

Where more than one base station controller (such as 18, 30, and 32) andmore than one mobile switching center (such as 16 and 24) are incommunication over the Ethernet passive optical network, differentmobile switching centers may handle the backhaul from different basestation controllers. For example, in an embodiment in which thedifferent base station controllers are operated by different wirelessservice providers, and different mobile switching centers are operatedby different wireless service providers, it is preferable for backhaulfrom each base station controller to be handled by the mobile switchingcenter corresponding to its own wireless service provider.

In an embodiment in which the Ethernet passive optical network handlesbackhaul from multiple service providers, it is desirable to providesecurity such that a service provider cannot access communications beinghandled by a different service provider. This may be handled indifferent ways.

In one embodiment, the Ethernet passive optical network uses wavelengthdivision multiplexing, in which each wavelength (lambda) is dedicated toa different wireless service provider. Each service provider is suppliedwith a gigabit Ethernet connection over its respective lambda. In suchan embodiment, transport bandwidth is shared between cell sites and MSCof only one operator per gigabit Ethernet (lambda) connection. In thisway, backhaul traffic from different wireless service providers iscombined on the same fiber cable, but each lambda is dedicated to asingle wireless service provider. Because there is no traffic sharing ofcommon Ethernet bandwidth and no foreign connections to other networks,the service is dedicated and secure without encryption.

In another embodiment, different service providers share backhaul overthe same gigabit Ethernet connection (and over the same lambda). In suchan embodiment, transport bandwidth is shared between wireless serviceprovider cell sites and mobile switching centers. In general, thisprovides less security than using a dedicated lambda for each wirelessservice provider. However, very good security can be provided byproviding separate pseudowire (PWE) backhaul circuits over the sharedlambda connection. In this embodiment, backhaul traffic of multiplewireless service providers is shared, but bandwidth is dedicated only towireless service provider operators with no foreign interconnection toother networks. Wireless service providers may wish to encrypt theirtraffic to guard against internal network attacks, leading to a minimaldelay in backhaul traffic.

A pseudowire circuit provides an emulation tunnel over a packet switchednetwork. Various services may be emulated over a pseudowire circuit,such as a frame relay, ATM (asynchronous transfer mode) circuits, or TDMsystems (time division multiplexing). One type of TDM system that may beemulated over a pseudowire circuit is a T1 system.

Using pseudowire circuits over an Ethernet passive optical network,legacy cell site equipment (such as base station controllers and basetransceiver stations) can be used to supply T1 signals to a pseudowiremultiplexer. The pseudowire multiplexer combines these signals intopackets for gigabit Ethernet communications, and the packets are sentover the passive optical network. With the addition of new repeaters inthe passive optical network, the backhaul facility is readily scalableto accommodate new base transceiver stations.

With the use of pseudowire circuits multiplexed over an Ethernet passiveoptical network, different service providers (or different equipmentfrom the same provider) that use different protocols can beaccommodated. For example, one service provider may use both EV-DO andT1 for backhaul. Another may make use of EV-DO Rev. A. These differentprotocols can be multiplexed together into a common lambda. For addedsecurity, each wireless service provider may have its own dedicatedpseudowire multiplexer.

II. An Exemplary EPON Backhaul System

One exemplary optical network backhaul system is illustrated in FIG. 2.In the system, a plurality of cell sites, such as site 40, are incommunication with one or more mobile switching centers, such as mobileswitching centers 42, 44, and 46. Communications are conducted over anoptical cable 48, which preferably is a bi-directional fiber link.

As shown in the example of FIG. 2, cell site 40 is provided with twobase transceiver stations 50 and 52. Backhaul from base stations 50 and52 is provided to the pseudowire multiplexer 54, which multiplexes thebackhaul onto optical cable 48. The multiplexers of FIG. 2 may includean electro-optical interface such as that described in U.S. PatentApplication Publication 2004/0052528 (Mar. 18, 2004).

Additional cell sites 56 and 58 are also provided in the backhaulsystem. Cell site 56 includes base transceiver stations 60 and 62 and amultiplexer 64. Cell site 58 includes base transceiver stations 66 and68 and a multiplexer 70. Additional cell sites, each associated with oneor a plurality of base transceiver stations, may likewise be provided inthe system. A cell site consisting of a single base transceiver station72, for example, may be connected on the optical network without theintermediation of a multiplexer.

In one embodiment, different base transceiver stations within the samecell site are associated with different mobile switching centers. Forexample, backhaul from base transceiver stations 50 and 66 may bedirected to one mobile switching center 42, while backhaul from basetransceiver stations 52 and 68 is directed to another mobile switchingcenter 46. This may be accomplished with at least two differenttechniques. In the first technique, making use of wavelength divisionmultiplexing, the multiplexers feed the backhaul from different basetransceiver stations onto different lambdas of the optical network. Inanother embodiment, the multiplexers provide different pseudowireconnections for the different base transceiver stations. These differentpseudowire connections may be provided on the same lambda.

The optical network backhaul system of FIG. 2 may further include one ormore third-party backhaul nodes, such as node 74. Such additional nodesmay be used, for example, to handle backhaul of data while mobileswitching centers handle voice backhaul.

Exemplary cell sites for use in the backhaul system of FIG. 2 areillustrated in FIGS. 3 and 4.

A cell site 76 as illustrated in FIG. 3 is preferably used inembodiments where backhaul from different base transceiver stations ismultiplexed into a single lambda. The cell site 76 includes two basetransceiver stations, 78 and 80, and a pseudowire multiplexer 82. Thebase transceiver stations 70 and 80 respectively communicate theirbackhaul to the pseudowire multiplexer 82 over 10 Mbps Ethernet backhaullinks 84 and 86. As an alternative, or in addition, one or more of thebackhaul links is provided over a T1 connection (88). In this example,base transceiver station 80 includes logic 90 for providing EV-DO and/orEV-DO Rev. A communications services, and the 10 Mbps backhaul link 86provides the backhaul for the EV-DO and/or EV-DO Rev. A services.

The cell site 76 further includes a repeater 92, which may be anoptical-electrical-optical (OEO) repeater. The pseudowire multiplexercombines backhaul communications from both base transceiver stations 78and 80 as separate pseudowire circuits on a single, shared gigabitEthernet connection 94. The repeater 92 then transmits the combinedgigabit Ethernet signal on a single lambda over the optical cable 96.

An alternative cell site 100 is illustrated in FIG. 4. It should benoted that the cell site 100 of FIG. 4 and the site 76 as illustrated inFIG. 3 may both be used together in the same optical backhaul network.The cell site 100 is preferably used in embodiments in which backhaulfrom different base transceiver stations is provided on differentlambdas of the optical network.

The cell site 100 includes two base transceiver stations, 102 and 104,and two respective pseudowire multiplexers 106 and 108. The basetransceiver station 102 communicates its backhaul over a 20 Mbpsbackhaul link to the multiplexer 106. The multiplexer 106 feed thebackhaul from base transceiver station 102 onto a gigabit Ethernet link118. The base transceiver station 104 is provided with EV-DO logic, thebackhaul from which is provided to the multiplexer 108 via a 10 MbpsEthernet backhaul link 112. The base transceiver station 104 furtherprovides voice backhaul over a T1 connection 114 to the multiplexer 108.In this way, voice backhaul over T1 and EV-DO backhaul over 10 MbpsEthernet can be combined in separate pseudowire circuits on a gigabitEthernet backhaul link 116. Backhaul from the gigabit Ethernet links 116and 118 can then be provided to the OEO repeater 120, which usesfrequency division multiplexing to combine the backhaul from links 116and 118 onto different lambdas of the optical network.

In an alternative embodiment, one or more of the cell sites in thebackhaul network may be accompanied by or replaced with an aggregationpoint that collects backhaul from base transceiver stations and/or cellsites at different locations.

The various mobile switching centers 42, 44, and 46, and any third partybackhaul node 74 communicate with corresponding base transceiverstations over the optical network. For example, where communicationsassociated with a particular service provider are assigned to aparticular corresponding lambda on the optical network, the mobileswitching center associated with that provider communicates using thatparticular lambda. Where communications associated with the serviceprovider are on a particular pseudowire link, the mobile switchingcenter communicates over that pseudowire link, even where the lambda onwhich the pseudowire link is established may be shared among otherservice providers.

As to communications reaching a mobile switching center that are notdestined for that mobile switching center, the mobile switching centermay itself operate as an OEO repeater. For example, if backhaul frombase transceiver station 60 (FIG. 2) is destined for the mobileswitching center 44, then base transceiver station 72, the mobileswitching center 46 (of a different service provider), and the cell site58 all relay the backhaul from base transceiver station 60 to mobileswitching center 44. As the backhaul is preferably encrypted, therelaying nodes cannot access the content of that backhaul.

The use of repeaters at cell sites and mobile switching centers allowsthe use of a daisy-chain and/or ring architecture, which can simplifythe provision of additional nodes in the backhaul network. Where a ringarchitecture is used, cell cites can be given a redundant physical linkwith mobile switching centers, enhancing reliability in case of physicaldisruptions. As additional cell sites are added to the backhaul network,or as additional base transceiver stations are added at these cellsites, the bandwidth allocations within an Ethernet passive opticalbackhaul network can be adjusted. Furthermore, the use of the Ethernetprotocol allows signaling to be shared on a fiber without requiringrouters or switches.

Another exemplary backhaul system is illustrated in FIG. 7. The exampleof FIG. 7 is similar to the example of FIG. 3, except that a synchronousoptical network (SONET) is provided in addition to the Ethernet passiveoptical network. In FIG. 7, a cell site 150 is provided with a basetransceiver station 152. The cell site 150 includes logic forcommunicating over 1XRTT (logic 154) and EV-DO Rev. A (logic 156). Thecell site 150 is further provided with a pseudowire multiplexer (PWE)158. The pseudowire multiplexer receives 1XRTT backhaul communicationsover a T1 line 160 and receives EV-DO backhaul communications over a 10BT Ethernet connection. The pseudowire multiplexer combines the backhaulsignals onto a fast Ethernet (FE) connection and supplies them to anEthernet passive optical network repeater 166.

From the repeater 166, the multiplexed backhaul is delivered over apassive optical network cable 168. At another passive optical networkrepeater 170, the backhaul is demultiplexed from the passive opticalnetwork and supplied over a fast Ethernet connection 172 to an E/SONET(synchronous optical network) ring transport network 174. An add/dropmultiplexer (ADM) 176 multiplexes the backhaul onto the SONET ring.

Another E/SONET add/drop multiplexer 178 recovers the backhaul signal bydemultiplexing it from the synchronous optical network. The backhaulsignal 180 is provided over a fast Ethernet connection 180 to apseudowire demultiplexer 182, which recovers the pseudowire circuitscontaining the 1XRTT and EV-DO backhaul signals. The demultiplexer 182in turn provides these backhaul signals to a mobile switching center184. The 1XRTT signals may be provided to the mobile switching centerover a T1 connection, while the EV-DO signals may be provided on a 10BTEthernet connection.

The embodiment of FIG. 7 allows an Ethernet passive optical network tobe used as a loop connecting multiple cell sites, while leveraging thetransport capabilities of an existing synchronous optical network. Theuse of pseudowire circuits allows end-to-end transmission of backhaulover different networks such as EPON or SONET while maintaining thelevel of service of the native backhaul protocol.

In the embodiment of FIG. 7, as in other illustrated embodiments,additional cell sites and repeaters (not illustrated) may be provided onthe passive optical network. These additional cell sites may beassociated with the same telecommunications service provider as cellsite 150, or they may be associated with one or more different serviceproviders. Similarly, additional mobile switching centers may beprovided on the SONET 174. These additional mobile switching centers mayassociated with either the same or different telecommunications serviceprovider as that associated with the mobile switching center 184.

III. An Exemplary Backhaul Method

A backhaul method, capable of being used with the systems of FIGS. 1-4,is illustrated in FIG. 5. The method of FIG. 5 may be used where a cellsite includes base transceiver stations from different serviceproviders, and where those service providers share a common lambda inthe backhaul network.

In step 122, the system receives a radio signal from a first mobile node(such as a mobile telephone 10). The first radio signal is received at afirst base transceiver station, which generates a backhaul signal instep 123. In step 124, the system receives a radio signal from a secondmobile node at a second base transceiver station, which generates abackhaul signal in step 125. The backhaul signals generated at the firstand second base transceiver stations include communications from,respectively, the first and second mobile nodes, but may also includecommunications from additional mobile nodes. Additional base transceiverstations may also be present within the cell site and generateadditional backhaul.

In step 126, the system multiplexes the backhaul from the two or morebase transceiver stations into separate pseudowire circuits on a gigabitEthernet link. In step 128, the combined signal is multiplexed onto anEthernet passive optical network. Backhaul signals from both basetransceiver stations are then present on the same lambda of the Ethernetpassive optical network, but on separate pseudowire connections.

The combined backhaul signals are received at a mobile switching centerin step 130. In the illustrated example, this mobile switching center isoperated by the telecommunications service provider that operates thefirst base transceiver station. The mobile switching centerdemultiplexes the first and second backhaul signals in step 132. In theembodiment of FIG. 5, the signals are demultiplexed from a single lambdausing a pseudowire demultiplexer. (In alternative embodiments, such asthat of FIG. 6, the backhaul signals are demultiplexed using awavelength division demultiplexer from different lambdas.) Because thismobile switching center is associated with the first base transceiverstation, it connects the backhaul from the first base transceiverstation to the public switched telephone network (PSTN) or othertelecommunications network in step 134. As to the backhaul from thesecond base transceiver station, the mobile switching center relaysthese communications over the Ethernet passive optical network in step136.

Another backhaul method capable of being used with the systems of FIGS.1-4, is illustrated in FIG. 6. The method of FIG. 6 may be used where acell site includes base transceiver stations from different serviceproviders, and where those service providers use different lambdas inthe backhaul network. Although the method is illustrated with respect tothe use of only two base transceiver stations, additional basetransceiver stations may also be present and employed in the method.

In step 138, a first base transceiver station receives a radio signalfrom a first mobile node. In step 140, a second base transceiver station(associated with a different service provider than the first station)receives a radio signal from a second mobile node. In steps 142 and 144the first and second base transceiver stations respectively generatefirst and second backhaul in Ethernet format. Using wavelength divisionmultiplexing, these Ethernet signals are multiplexed onto separatelambdas of the Ethernet passive optical network in step 146.

In an alternate implementation of the method of FIG. 6, the multiplexingof step 146 may be performed with a pseudowire multiplexer, and thepseudowire circuits corresponding to Ethernet signals from the differentbase transceiver stations are provided on either the same or differentlambda of the Ethernet passive optical network.

The method illustrated in FIG. 6 may be continued with step 130 of FIG.5. That is, after the different backhauls are multiplexed on theEthernet passive optical network (FIG. 6, step 146), the backhaulsignals may be relayed and/or processed by mobile switching centers asappropriate, as in steps 132-136.

The foregoing embodiments are provided as examples of the system andmethod of the invention, and the invention is not to be taken as limitedto those examples. Instead, the invention is defined by the followingclaims.

The invention claimed is:
 1. A backhaul method comprising: receiving afirst radio signal at a first base transceiver station; receiving asecond radio signal at a second base transceiver station; generating afirst backhaul signal from the first radio signal; generating a secondbackhaul signal from the second radio signal; multiplexing the first andsecond backhaul signals into respective first and second pseudowireconnections on an Ethernet passive optical network, wherein the firstbase transceiver station communicates with a first mobile switchingcenter over the first pseudowire connection, and the second basetransceiver station communicates with a second mobile switching centerover the second pseudowire connection; receiving the first backhaulsignal and the second backhaul signal at a first mobile switchingcenter; relaying the second backhaul signal from the first mobileswitching center to the second mobile switching center; and receivingthe relayed second backhaul signal at the second mobile switchingcenter; wherein the first base transceiver station and the first mobileswitching center are operated by a first service provider; and whereinthe second base transceiver station and the second mobile switchingcenter are operated by a second service provider different from thefirst service provider.
 2. The method of claim 1, wherein multiplexingincludes providing the first and second backhaul signals on separatelambdas of the Ethernet passive optical network.
 3. The method of claim1, wherein the first and second pseudowire connections are sent over thesame lambda of the Ethernet passive optical network.
 4. A backhaulmethod comprising: receiving a first radio signal at a first basetransceiver station; generating a first backhaul signal from the firstradio signal; sending the first backhaul signal on a first pseudowireconnection on a passive optical network; receiving a second radio signalat a second base transceiver station different from the first basetransceiver station; generating a second backhaul signal from the secondradio signal; sending the second backhaul signal on a second pseudowireconnection on the passive optical network; receiving and processing thefirst backhaul signal at a first mobile switching center; receiving thesecond backhaul signal at the first mobile switching center, andforwarding the second backhaul signal to a second mobile switchingcenter; and receiving and processing the forwarded second backhaulsignal at the second mobile switching center; wherein the first basetransceiver station and the first mobile switching center are operatedby a first service provider; and wherein the second base transceiverstation and the second mobile switching center are operated by a secondservice provider different from the first service provider.
 5. Themethod of claim 4, wherein the first and second base transceiverstations are provided at a single cell site, and wherein sending thefirst and second backhaul signals includes: multiplexing the first andsecond backhaul signals onto separate pseudowire circuits; and providingthe separate pseudowire circuits over a single lambda of the passiveoptical network.
 6. The method of claim 5, wherein the passive opticalnetwork is an Ethernet passive optical network.
 7. The method of claim4, wherein the first and second base transceiver stations are providedat a single cell site, and wherein sending the first and second backhaulsignals includes: providing the first backhaul signal on a first lambdaof the passive optical network; and providing the second backhaul signalon a second lambda of the passive optical network, wherein the secondlambda is different from the first lambda.
 8. The method of claim 4,wherein the passive optical network is an Ethernet passive opticalnetwork.
 9. The method of claim 4, wherein the first and second basetransceiver stations are at different locations, and wherein sending thefirst and second backhaul signals is performed at an aggregation point.